1) Field of the Disclosure
The disclosure relates generally to composite reinforcing support structures, and more specifically, to composite hat stiffener configurations and methods used in forming composite hat-stiffened pressure webs, such as for use in aircraft.
2) Description of Related Art
Composite structures are used in a wide variety of applications. In aircraft construction, composites are used in increasing quantities to form the fuselage, wings, tail section and other components. For example, aircraft fuselage structures, such as bulkheads and pressure decks, may be formed of composite stiffened panel structures comprising composite pressure web or skin panels to which reinforcing stiffeners may be attached or bonded to improve the strength, stiffness, buckling resistance, and stability of the composite pressure web or skin panels. The reinforcing stiffeners attached or bonded to the composite pressure web or skin panels may be configured to carry various loads.
Known reinforcing stiffeners used with such composite pressure web or skin panels may include I-beam stiffeners (a beam with an I-shaped cross-section). However, known I-beam stiffened composite panels reinforced with such known I-beam stiffeners may experience high pull-off loads at the radius filler, i.e., “noodle”, portions of the I-beam stiffener or at the radius common to the attached flange of the reinforcing stiffener in the region of the noodle. As used herein, “pull-off load” means a shear load and/or moment force applied to a composite component part, such as a reinforcing stiffener, at locations where the composite component part is attached or bonded to a structure, such as a composite pressure web or skin panel, such that the shear load and/or moment force may cause delamination or separation of the reinforcing stiffener from the attached structure. As used herein, “radius filler noodle” means a composite material or adhesive/epoxy material having a triangular cross-section that is used to fill a gap left by the radius of curved pieces of a composite component part, such as a reinforcing stiffener.
To decrease the likelihood of delamination or separation of the I-beam stiffener from the composite pressure web or skin panel due to high pull-off loads, numerous additional radius filler elements, fasteners, and/or angle fittings may be required at the locations or joints where the I-beam stiffener is attached or bonded to the composite pressure web or skin panel. Such radius filler elements, fasteners, and/or angle fittings may provide additional structural reinforcement to the locations or joints and distribute the shear load and/or moment force in order to reduce the risk of delamination at the radius filler or noodle portions of the I-beam stiffener.
However, the use of such numerous additional radius filler elements, fasteners, and/or angle fittings may result in increased production time, increased part count and expense, increased labor and manufacturing costs to install and maintain the parts, and an overall increase in the complexity of the structure. Moreover, the use of fasteners or angle fittings that require mechanical fastening to the reinforcing stiffener or composite pressure web or skin panel may require the formation of appropriately-sized holes in the composite material or structure. This, in turn, may require the use of specialized tooling to form such holes in the composite material or structures. Such specialized tooling may result in further increased labor and manufacturing costs.
Accordingly, there is a need in the art for an improved composite stiffener and improved composite stiffened structures and methods of making the same that provide advantages over known configurations, structures and methods.